Seismic records show that under the Yellowstone geyser, a large egg-shaped chamber is connected to the mouth of Old Faithful by a sort of pipe. After every eruption, water levels rise in the chamber and send steam bubbles into the conduit—which creates a "bubble trap" that leads to the eventual steam explosion.

What's the big deal?

The finding helps discredit an old idea that large geysers are fed by long, narrow tubes (Our Amazing Planet describes Old Faithful's "plumbing [as] more like a bagpipe than a flute").

Researchers made a similar finding earlier this year in Russia, where geysers are also fed by caverns that create bubble traps.

Another neat fact: Scientists were able to map Old Faithful's cavern with seismic records because gas bubbles create tremors when they pop.

And there's good news for those eager to visit it: Sequestration forced the park to postpone its annual snow-plowing efforts, pushing the opening date to April 26; but the Billings Gazette reports that the road to Old Faithful opened Friday, due to a happy combination of good weather, less snow than expected, and help from the state's Department of Transportation.

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